A large amount of interest has arisen as a result of environmental pollution concerns on treatment of municipal and industrial wastewaters. As a result of federal, state and local regulations as well as concerns on protecting the environment, a large amount of research and development effort has gone into the treatment of wastewater from various sources and particularly wastewater arising from industrial facilities. Often in treatment of wastewater from industrial and municipal sources, the activated sludge process has been employed conventionally for treatment and purification to the extent that the treated water can be reused or returned to the environment. Where wastewater arises from industrial operations, the wastewater can contain problem contaminants, in general not normally found in wastewater from municipal sources, and these include industrial wastewaters containing as contaminants, ammonia, cyanide, thiocyanate, sulfide and organic materials, even of a complex nature. Further, industrial wastewaters can contain contaminants at concentrations which significantly exceed those found in wastewaters from municipal sources.
In particular, wastewaters which contain ammonia as a contaminant are produced in a wide variety of industrial operations and problems presently exist in appropriately treating wastewaters where the wastewater contains a high concentration of ammonia. It is economically advantageous therefore to develop treatment procedures for wastewaters which, in raw form, contain not only ammonia in high concentrations, but typically a wide variety of contaminants other than ammonia. In fact, where wastewaters contain high concentrations of ammonia, state-of-the-art systems conventionally employed to treat these wastewaters to render them environmentally acceptable for discharge into the ecosphere are complex and extremely expensive.
To illustrate this further, raw wastewater containing high concentrations of ammonia can arise in industrial processing in coke plants, petroleum refineries, oil shale retorting, coal gasification processes and coal liquefaction processes. Ammmonia-containing wastewaters can also arise from pharmaceutical processing, munitions manufacture, food processing and fertilizer manufacture. Typical compositions of contaminants present in one illustrative subset of typical wastewaters containing high concentrations of ammonia are shown in Table 1 below.
TABLE 1 ______________________________________ TYPICAL CONTAMINATS AND THEIR CONCENTRATIONS IN REPRESENTATIVE INDUSTRIAL WASTEWATERS Typical Wastewater Composition (mg/l) Wastewater Phen- Source NH.sub.3 COD olic CN.sup.- SCN.sup.- S.sup.= ______________________________________ By-product 1,800 2,500 400 10 100 200 Coking to to to to to to 6,500 10,000 3,000 100 1,500 600 Petroleum 1,000 N.A. 100 N.A. N.A. 275 Refining to to to 7,000 1,000 11,000 Oil Shale 1,000 8,100 .about.45 0 .about.55 20 Retorting to to to to 7,300 10,800 21 220 Coal Gasification Slagging 2,000 7,000 1,400 4 15 100 Lurgi Process to to to to to to 17,000 21,000 4,000 15 300 500 Hygas 2,600 3,000 560 0.1 17 60 Process to to to to to to 4,600 5,000 900 0.7 45 220 Grand Forks 4,000 21,000 3,500 1 80 60 Energy Tech. to to to to to to Center 7,500 30,000 6,000 50 200 300 Gasifier Coal Liquefaction Solvent Ref. .about.13,000 .about.6,000 .about.1,900 N.A. N.A. .about.5,000 Coal-Proc-I ______________________________________
It can be seen from the wastewater compositions shown in Table 1 above, that ammonia concentrations in these raw wastewaters are high and can range from a low of 1,000 to nearly 20,000 mg/l. Typically, these industrial wastewaters also contain significant concentrations of other contaminants, including (1) a range of organics from benzene, toluene, xylenes to phenols to higher molecular weight compounds, (2) cyanide and thiocyanate and (3) various sulfur compounds.
Environmentally acceptable control approaches presently employed in commercial practice are of basically two types--(1) physical/chemical treatment and (2) combined pretreatment and biological processing. A large amount of interest has recently been developed in the biological treatment of these high strength ammoniacal wastewaters.
The approaches conventionally used to treat wastewater containing contaminants as indicated above where treatment by biological processing is involved generally require three major processing steps in addition to a basic biological processing step. Conventional practice and treatment of wastewaters containing contaminants as indicated above are shown schematically in FIG. 1. As can be seen from an examination of FIG. 1 showing conventional practice relating to treatment of wastewaters containing high levels of ammonia as well as other contaminants, the treatment stages include at least: (1) wastewater pretreatment for removal of ammonia, hydrogen sulfide, and possibly phenols, (2) recovery/disposal of ammonia, hydrogen sulfide, and in certain cases, phenols, (3) pretreated wastewater treatment in an activated sludge biological wastewater treatment process, and (4) waste sludge processing, which can include sludge conditioning, microbiological and possibly lime sludge processing, and disposal. The need for expensive pretreatment steps and by-product recovery steps results from the universally accepted conventional thinking that activated sludges cannot treat significant concentrations of ammonia in feed wastewater. Conventional practice also frequently dictates a significant and expensive sludge wastage or discharge rate for proper operation of the activated sludge process. The net result of this conventional thinking is an extremely complex and expensive state-of-the-art system for biologically based treatment of wastewaters containing high concentrations of ammonia and also high concentrations of sulfide.
Although different biological treatment systems have been designed and operated, basically known techniques have not been completely successful in treating, particularly biologically, wastewaters such as those from industrial sources in which hazardous contaminants or contaminants at high levels are present. These techniques, in particular, have not been suitable for treatment of industrial waste-waters containing, particularly, a high concentration of ammonia.
In treating wastewaters containing ammonia, it is known that certain aerobic autotrophic microorganisms can oxidize ammonia to nitrite and that nitrite can be further microbially oxidized to nitrate. This reaction sequence, viz., oxidation of ammonia to nitrate, is known in the art as nitrification and the responsable microorganisms are: Nitrosomonas and Nitrobacter. More specifically, Nitrosomonas, are known to oxidize ammonia to nitrite in aqueous systems in which (1) dissolved oxygen levels are in excess of approximately 0.5 mg/l (as disclosed in H. E. Wild et al, "Factors Affecting Nitrification Kinetics", J. Water Pollut. Cont. Federation, 43, 1845-1854 (1971)) and (2) free ammonia in solution is held below about 10 to 150 mg/l (as disclosed in Anthonisen et al, "Inhibition of Nitrification by Ammonia and Nitrous Acid", J. Water Pollut. Cont. Federation, 48, 835-852 (1976)). Nitrosomonas microorganisms are ubiquitous in the environment and seed for the development of a Nitrosomonas population in a sludge is therefore available from a wide variety of sources. Both Nitrosomonas growth rates and their ammonia-nitrogen oxidation reaction rates are a function of solution temperature, pH and dissolved oxygen levels. For example, a reaction rate of about 2.4 mg nitrogen oxidation per mg of microorganism per day at a temperature of 20.degree. C., a pH of 7.0 and a dissolved oxygen level of between 1 and 2 ppm has been reported. (See G. M. Wong-Chong, "Kinetics of Microbial Nitrification as Applied to the Treatment of Animal Wastes", Ph.D. Thesis, Cornell University, 1974.)
Further, Nitrobacter are known to oxidize nitrite to nitrate in aqueous systems where the dissolved oxygen level is in excess of approximately 0.5 mg/l (see H. E. Wild et al, supra.) and free ammonia in solution is held below about 0.1 to 10 mg/l and free nitrous acid in solution is held below about 0.2 to 2.8 mg/l (see Anthonisen et al, supra.). Nitrobacter microorganisms are ubiquitous in the environment also and seed for development of a Nitrobacter population in a sludge is therefore available from a wide variety of sources. Both Nitrobacter growth rates and their nitrite reaction rates are a function of solution temperature, pH and dissolved oxygen levels. For example, a reaction rate of about 7.0 mg nitrogen oxidation per mg of microorganism per day at a temperature of 20.degree. C., a pH of 7.0, and a dissolved oxygen level of between 1 and 2 ppm has been reported (see Wong-Chong, supra.).
Complete elimination of ammonia entails the oxidation to nitrite and/or nitrate followed by reduction of the nitrite and/or nitrate to nitrogen gas. This latter reduction of the nitrite and/or nitrate to nitrogen gas is generally known in the art as denitrification and the reaction of reduction of nitrite and/or nitrate to free nitrogen is mediated by facultative heterotrophic microorganisms generally of the genera of Pseudomonas, Achromobacter, Bacillus and Micrococcus. These microorganisms are capable of oxidizing organic matter by utilizing oxygen and, in the absence of oxygen, they can use nitrite and/or nitrate, if present. Facultative heterotrophic microorganisms are further ubiquitous in the environment and seed for development of populations in a sludge is therefore available from a variety of sources. Facultative heterotrophic microorganism growth rates and denitrification reaction rates and a function of solution temperature, pH and ratio of dissolved oxygen to nitrite/nitrate oxygen availability. For example, a denitrification reaction rate of about 0.6 mg nitrogen oxidation per mg of microorganism per day with methanol as an organic at a temperature of 20.degree. C. and a pH of 8 to 9 in the absence of dissolved oxygen has been reported (see R. P. Michael, "Optimization of Biological Denitrification Reactors in Treating High Strength Nitrate Wastewater", M.S. Thesis, University of Vermont, May 1973).
Frequent references are also made in the literature to unexplained nitrogen losses from basically aerobic sludges (e.g., as disclosed in K. Wuhrmann, "Effect of Oxygen Tension on Biochemical Reactions in Sewage Purification Plants" in "Advances in Biological Waste Treatment", W. W. Eckenfelds, Jr. and B. J. McCabe, Eds., Pergamon Press (1963); Barth et al, "Nitrogen Removal by Municipal Wastewater Treatment Plants", J. Water Pollut. Cont. Federation, 38, 7 (1966); and D. C. Climenhage, "Nitrogen Removal for Municipal Wastewater", Project No. 72-5-15, Ontario Ministry of the Environment (1975)). It has been speculated that these losses are due either to spurious amounts of "anaerobic" denitrification which occur in random localized "dead spots" in the sludge where dissolved oxygen levels have fallen to zero or to "aerobic" denitrification. In fact, in 1977, the inventor of the invention described and claimed herein speculated that "aerobic" denitrification does occur and is favored by high microbial sludge concentrations, low dissolved oxygen levels of about 1 ppm and a solution pH of 7.0 (see G. M. Wong-Chong et al, "Advanced Biological Oxidation of Coke Plant Wastewaters for the Removal of Nitrogen Compounds", Carnegie-Mellon Inst. of Research Report to the American Iron and Steel Institute, (April 1977)). As a theoretical explanation, Wong-Chong, supra, postulated a porous microorganism particle model with oxygen gradients such that some portion of the core of the basically aerobic particle is anoxic. Others have speculated similarly regarding the existence of "aerobic" denitrification. (See, for example, L. B. Wood et al, "Some Observations on the Biochemistry and Inhibition of Nitrification", Water Research, 5, 543-551 (1981); I. Murray et al, "Interrelationships between Nitrogen Balance, pH and Dissolved Oxygen in an Oxidation Ditch Treating Farm Animal Waste, Water Research, 9, 25-30 (1975); and J. P. Voets, et al, "Removal of Nitrogen from Highly Nitrogenous Wastewaters", Journal of the Water Pollution Control Federation, 47, 394-398 (1975)).
The above biologically mediated processes of nitrification and denitrification, and conversion of ammonia to free nitrogen using Nitrosomonas, Nitrobacter and facultative microorganisms are well known. However, there is a large economic incentive for improvements in conventional approaches to treating wastewater containing high levels of ammonia and other contaminants. Research and development to upgrade the performance of biological treatment systems to handle high ammonia strength liquors has been extremely limited and has been basically considered unsuccessful.
With the exception of the speculations discussed above on how "aerobic" denitrification could possibly occur, all of the other prior art basically discredits the serious possibility of controllably achieving simultaneous nitrification and denitrification from a single sludge. In fact, the prior art has basically set forth that nitrification/denitrification conditions are thermodynamically antagonistic and as such, nitrification should be separated from denitrification (see Bishop et al, "Single-stage Nitrification-Denitrification", J. Water Pollut. Cont. Federation, 48, 521-531 (1976)).
Numerous possible permutations and combinations, which can be logically considered of multi-reaction step nitrification/denitrification systems, have been postulated in the literature. These, however, have been largely for application to the processing of low ammonia strength municipal sewage waste (see Bishop et al, supra.; Climenhage, supra, Barth et al. "Chemical-Biological Control of Nitrogen and Phosphorus in Wastewater Effluent", J. Water Pollut. Cont. Federation, 40, 2040-2054 (1968); and J. L. Barnard, "Biological Nutrient Removal Without the Addition of Chemicals", Water Research, 9, 485-490 (1975)). Only two literature references are known (see Barker et al, "Biological Removal of Carbon and Nitrogen Compounds from Coke Plant Wastes", EPA Report EPA R2-73-167 (April 1973); and P. D. Kostenbader et al, "Biological Oxidation of Coke Plant Weak Ammonia Liquor", J. Water Pollut. Cont. Federation, 41, 199-207 (1969)) in which high strength ammonia containing wastewater was treated and of these only Barker et al, supra, attempted to achieve nitrification and denitrification. All other attempts to achieve nitrification or a combination of nitrification and denitrification, including that of the inventor herein prior to this invention, have been performed on weak-ammonia coke plant wastewater, i.e., wastewater from a coke plant from which a significant fraction of the ammonia has been stripped. High nitrification efficiencies for ammonia-stripped coke wastewater in a one-stage biological reactor with extended solids residence times has been reported (see A. Bhattacharyya et al, "Solids Retention Time--A Controlling Factor in the Successful Biological Nitrification of Coke Plant Waste", Proc. 12th Mid-Atlantic Industrial Waste Conference, Bucknell University, Lewisburg, Pa. (July 1980)).
Further, variable success with a two-stage nitrification-denitrification reactor system on ammonia-stripped coke wastewater has also been reported (T. R. Bridle et al, "Biological Treatment of Coke Plant Wastewaters for Control of Nitrogen and Trace Organics", Presentation at 53rd Annual Water Pollution Control Federation Conference, Las Vegas (September 1980)). Moderate success in nitrifying ammonia-stripped coke wastewater has also been reported by the inventor of the invention described and claimed herein (see Wong-Chong et al, supra.). Variable success has also been reported on a two-stage nitrification-denitrification reactor system on ammonia-stripped coke wastewater (see S. G. Nutt et al, "Two Stage Biological Fluidized Bed Treatment of Coke Plant Wastewater for Nitrogen Control, "Presentation at the 54th Annual Water Pollution Control Federation Conference, Detroit (October 1981)).
After experimental attempts to biologically treat coke wastewaters containing high ammonia concentrations directly, Kostenbader et al, supra, in experimental work to establish at what ammonia concentrations performance of microorganisms on wastewaters containing cyanide, thiocyanate and COD was affected, concluded that ammonia concentrations in excess of about 2,000 mg/l seriously inhibited the overall performance of biological sludge. In an extremely complex three-stage reaction system (two aerobic stages in series followed by an anaerobic stage), Barker et al, supra, treated high strength coke plant wastewaters were treated for 352 days. Unfortunately, this program led to unsuccessful results. Typical feed ammonia strengths achieved during these experiments were less than 300 mg/l of ammonia (corresponding to about 12-fold dilution of the raw ammonia-containing feed wastewater to be treated) with substantially less than complete nitrification and denitrification. Highest feed ammonia strengths achieved were about 1200 mg/l ammonia (corresponding to a 3-fold dilution with respect to the raw wastewater feed). Treatment at these levels was sustained only for a single two-week period in the entire test program. Highest nitrification and denitrification rates achieved during this relatively high ammonia strength test period were only between 10% and 50%. In view of the results obtained, the project was abandoned.